The present invention relates to a method for reconstructing a femoral portion of a knee in a total knee replacement of both the medial and lateral condyles. More particularly, the present invention relates to a method in which the femoral component of reconstructed knee presents both the lateral and medial condyles at substantially the same distal position as the original natural lateral condyle to locate the intercondylar notch and distal patellar groove in a position generally coinciding with the natural intercondylar notch and distal patellar groove being replaced.
The proximal/distal placement of the femoral component in total knee arthroplasty is critical for duplicating the kinematics of the knee with the arthroplasty. Several authors have recommended that the joint line (transverse axis) of the arthroplasty should be at approximately the same proximal/distal position as the joint line (transverse axis) of the normal knee. Most surgical techniques recommend that an amount be resected off the distal femur roughly equal to the thickness of the femoral prosthesis, doing so will restore the joint line to substantially its original position. This is actually too simplistic an analysis of a complex situation. For example, sometimes there is wear of the distal condyles and osteophytes can deform the distal condyles. Thus, the original cartilage covered surface, which represents the original distal femoral surface, is usually not available for referencing at the time of surgery. More importantly, the average transverse axis (joint line) is tilted 3.degree. with respect to the mechanical axis of the knee. This is because the medial femoral condyle is more distally placed than the lateral femoral condyle in the normal knee. Most authorities today recommend that the transverse axis of the reconstruction be made perpendicular to the mechanical axis. Thus, the original transverse axis is tilted 3.degree. and the reconstructed transverse axis is made perpendicular to the mechanical axis.
In an arthritic valgus knee the medial femoral condyle is usually much more distally placed than the lateral femoral condyle due to wear or lateral femoral condyle hypoplasia. In an arthritic varus knee there has usually been some wear of the medial femoral condyle, but in most cases, despite this wear, the medial femoral condyle is still more distally placed than the lateral femoral condyle. In both varus and valgus knees the reference condyle for distal femoral resection is presently the medial condyle.
The distal femur actually has three different surfaces for articulation. There is the medial femoral condyle, the lateral femoral condyle, and the central portion of the distal femur against which articulates the patella. The distal femur, obviously, has articulating against it both the tibia and the patella. The proximal/distal placement of the patella/femoral joint is just as important, and perhaps even more important, than the proximal/distal placement of the tibial/femoral joint.
If a surgeon has an 8 mm thick femoral component and resects 8 mm off the distal medial femoral condyle, in almost all knees the surgeon resects several millimeters less of distal lateral condyle. If the surgeon then installs an 8 mm femoral component, the knee has a lengthened lateral femoral condyle and a lengthened intercondylar notch which defines the patella/femoral joint line. In other words, the new joint line has been placed at approximately the level of the original medial femoral condyle but has been placed distally with respect to the original lateral femoral condyle.
This lengthening of the lateral femoral condyle requires the patella to move more distally with respect to the femur as the patella moves to the distal aspect of the femur in the extremes of flexion. This requires more stretching of the quadriceps mechanism and higher patella load. This may make the patella more likely to dislocate and increase the likelihood of subluxation. The higher patella load may also be the cause of some lateral pain and may contribute to patella fractures.
In contrast to the above known method, the present invention reconstructs the distal joint surface of the knee at approximately the distal level of the original lateral femoral condyle. One advantage of reconstructing the knee at the level of the original lateral femoral condyle is that it gives more room for the tibial component. The tibial base plate should be adequately thick for strength and the tibial plastic bearing insert should be adequately thick for wear considerations. There is a problem with space in the reconstruction. If a surgeon lengthens the lateral femoral condyle it aggravates the space problem. Reconstructing the knee at the level of the lateral femoral condyle leaves more room for a tibial component and minimizes the tibial resection level. In addition, a thicker plastic tibial bearing may be used with the present invention. As the thickness of the bearing increases, internal stresses tend to decrease.
The instruments of the present invention resect 3 mm of bone from the intercondylar notch area preferably using the notch as a reference point. Each femoral component of the present invention is approximately three millimeters thick in the patellar groove area, regardless of the size of the component. Therefore, the distal patellar groove of the prosthetic femoral component of the present invention is anatomically positioned at about the same distal position as the groove in the normal knee. Accordingly, the patella must travel only its original distal excursion distance during normal knee flexion.
Of course, large bones have deeper notches than small bones since bones are proportionately sized. A three millimeter depth of resection in the notch area in a small bone will remove less distal femoral condyle than a three millimeter depth of resection in the intercondylar area for a large bone. The present invention provides a plurality of femoral components having distal femoral condyles which gradually become thicker with size proportionally to compensate for the varying amounts of the distal femoral condyles which are resected.
The present invention preferably uses the intercondylar notch as a reference point for guiding resection of the distal end of the femur. The notch reference is not affected by condyle hypoplasia which can occur both to the medial and the lateral femoral condyle and it is typically not affected by wear of an individual condyle. The notch area is rarely worn, although occasionally osteophytes do form that need to be resected. In the valgus knee with a hypoplastic lateral femoral condyle the notch area is not hypoplastic. The lateral femoral condyle resection level in such cases gives the desired lengthening of the lateral femoral condyle in that type of knee. Referencing the intercondylar notch for proximal/distal placement of the femoral component consistently and accurately reconstructs the patella/femoral joint at its appropriate proximal/distal level. This results in the tibial/femoral component joint being reconstructed at also its proper proximal/distal level but without the problems of severe anatomical variations and severe bony erosion. The notch reference point is a more convenient and reliable reference point for proximal/distal placement of the femoral component than the distal femoral condyle reference point.
Another issue which relates to this is the rotational position of the femoral component. The medial femoral condyle is larger than the lateral femoral condyle and for proper femoral rotation, usually a larger piece of bone needs to be resected off the posterior medial femoral condyle than the posterior lateral femoral condyle. This results in a relatively more externally rotated position of the femoral component with respect to the femur and provides better patella tracking. The patella tracks better with this maneuver and is less likely to dislocate and the knees flex better and are more stable. Fewer lateral releases are needed and fewer revisional surgeries are needed for patellar subluxation and dislocation. The instruments of the present invention have a built-in 3.degree. of external rotation.
The method and apparatus of the present invention involves resecting the distal medial and lateral condyles in a plane generally perpendicular to the mechanical axis of the femur at a predetermined distance proximal to the intercondylar notch preferably using the notch as a reference. Then a femoral component is selected to have a size and thickness to present both the medial and lateral condyles at the same general distal position as the original natural lateral condyle being replaced. This selecting step involves selecting an appropriate size femoral component from a group of components having varying sizes and condyle thicknesses.
The present invention preferably uses the intercondylar notch as a reference point for distal condylar resection. However, it is understood that other reference points can be used in order to reestablish the patella femoral groove at the same location as the natural knee and to reestablish the medial and lateral condyles at the same general distal position as the original natural lateral condyle being replaced. The reference points include the medial condyle and the lateral condyle as well as the intercondylar notch.
It is not new to use the intercondylar notch as a reference point for distal condylar resection per se. Prior art systems have used the notch as a reference point from which to make the distal condylar resection. For instance, in one system designed by Buechel & Pappas, the first resection is a resection of the proximal end of the tibia to provide a tibia platform. This resection is made with typical tibial instrumentation. Then, the anterior and posterior femur condyles are resected independent of the notch. Then, referencing the intercondylar notch, Buechel & Pappas resect the distal end of the femur.
Other systems including DePuy's F.I.R.S.T. system introduced in mid-1980s also use the intercondylar notch as a reference point for making the distal femoral resection, but this system does not try to reconstruct the natural lateral condyle being replaced. Also, in DePuy's F.I.R.S.T. system, the femoral implants were not proportioned in size and thickness to place both the medial and lateral condyles of the natural distal position generally corresponding to the original lateral condyle.
The present invention involves selecting a femoral component to place both the medial and lateral condyles at the same level, but at the same level as the original lateral condyle. The method of the present invention therefore, is an advancement over the prior art methods and apparatus because the new method recreates the lateral condyle joint line versus the medial condyle joint line. The present invention reestablishes the original natural distal patellar groove in which the patellar articulates at the same general position as the natural distal patellar groove. This improvement places less strain, wear and tear on the patellar tendon and potentially reduces soft tissue releases for proper tracking of the patellar mechanism.
It is an object of the present invention to provide a method for reconstructing a femoral portion of a knee in a total knee replacement of both the medial and lateral condyles so that the reconstructed knee presents the lateral and medial condyles at the same general distal position as the original natural lateral condyle and locates the intercondylar notch and distal patellar groove in a position generally coinciding with the natural notch and groove.
According to one aspect of the present invention, a method is disclosed for reconstructing a femoral portion of a knee in a total knee replacement of both the medial and lateral condyles to locate the intercondylar notch and distal patellar groove of the reconstructed knee in a position generally coinciding with the natural intercondylar notch and distal patellar groove. The method includes the steps of resecting the distal medial and lateral condyles to form a resected distal surface, selecting a femoral component sized to have an intercondylar notch and distal patellar groove at the same general distal position as the original natural intercondylar notch and distal patellar groove being replaced, and installing the selected femoral component on the resected distal surface.
In the illustrated embodiment, the plane of the resected distal surface is generally perpendicular to the mechanical axis of the femur. The resected distal surface is spaced apart a predetermined distance proximal from the intercondylar notch using the intercondylar notch as a reference. However, other reference points may be used.
The femoral component has a thickness in the area of a patellar groove substantially equal to said predetermined distance so that the distal patellar groove of the femoral component is positioned at substantially the natural location of the distal patellar groove. The selecting step includes the steps of providing a plurality of femoral components having various anterior/posterior lengths and increasing distal and posterior condyle thicknesses as the anterior/posterior length increases and determining which of the plurality of femoral components has an appropriate distal and posterior condyle thickness to approximate the natural distal position of the resected lateral condyle.
According to another aspect of the present invention, a method is disclosed for reconstructing a femoral portion of a knee in a total knee replacement of both the medial and lateral condyles so that both the medial and lateral condyles of the reconstructed knee are located at about the same distal position as the original natural lateral condyle. The method includes the steps of resecting the distal medial and lateral condyles to form a resected distal surface, selecting a femoral component sized to have both the medial and lateral condyles at the same general distal position as the original natural lateral condyle being replaced, and installing the selected femoral component on the resected distal surface.
The selecting step includes the step of providing a plurality of femoral components having various anterior/posterior lengths and increasing distal and posterior condyle thicknesses as the anterior/posterior length increases and determining which of the plurality of femoral components has an appropriate distal and posterior condyle thickness to approximate the natural distal position of the resected lateral condyle. The determining step illustratively includes the step of placing a sizer assembly on the resected end of the femur to indicate which one of the plurality of femoral components is appropriately sized for the resected femur.
The resected distal surface is spaced apart a predetermined distance proximal from the intercondylar notch. The femoral component has a thickness in the area of a patellar groove substantially equal to said predetermined distance so that the distal patellar groove of the femoral component is positioned at substantially the natural location of the distal patellar groove.
According to yet another aspect of the present invention, a method is provided for reconstructing a femoral portion of a knee in a total knee replacement, the distal end of which has medial and lateral condyles and an intercondylar notch therebetween defining a distal patellar groove for the articulation of the patella with the femur during flexion of the knee. The method includes the steps of locating and drilling a hole in the intercondylar notch to access an intermedullary canal of a femur, installing a femoral alignment guide onto an intermedullary rod, and inserting the intermedullary rod through said hole toward a proximal end of the femur. The method also includes the steps of moving said femoral alignment guide into contact with the intercondylar notch of the knee, positioning a femoral cutting block relative to the alignment guide, and securing the cutting block to the femur to align a guide surface of the cutting block at a predetermined proximal distance from said intercondylar notch. The method further includes the steps of removing the femoral alignment guide and rod from the femur, resecting the distal lateral and medial condyles using the guide surface of the resection block as a resection reference, and determining an appropriate size of a femoral component having a size and condyle thickness which will reconstruct the lateral condyle and position the distal patellar groove at about the same distal locations to approximate the anatomy of the natural knee being replaced and to position the medial condyle of the femoral component at the same distal position as the original lateral condyle.
In the one illustrated method, the step of moving the femoral alignment guide into contact with the intercondylar notch of the knee includes the step of positioning an intercondylar saddle on the alignment guide in engagement with the intercondylar notch. The step of positioning the femoral cutting block relative to the alignment guide includes the step of positioning the cutting block on an arm of the alignment guide at a selected position spaced apart from the intercondylar saddle by predetermined distance so that the femur is resected a predetermined distance proximal to the intercondylar notch. The step of determining an appropriate size of a femoral component includes the step of placing a sizer assembly on the resected distal end of the femur to determine an appropriate size femoral component.
According to still another aspect of the present invention, an alignment guide is provided for positioning a saw guide surface of a cutting block at a predetermined position proximally from an intercondylar notch of a femur having an intermedullary rod extending along its anatomical axis. The alignment guide includes a body portion formed to include an aperture for receiving the rod therethrough, and an arm coupled to the body for receiving the cutting block thereon. The alignment guide also includes means for securing the cutting block to the arm at a predetermined position relative to the body, and an intercondylar saddle coupled to the body portion of the alignment guide, the saddle being configured to engage the intercondylar notch of the femur to align the cutting block coupled to the arm of the alignment guide at said predetermined position proximal to the intercondylar notch.
The saddle is configured to surround the aperture for receiving the intermedullary rod. The saddle permits limited movement of the alignment guide relative to the intermedullary rod to permit the alignment guide to be seated at the deepest section of the intercondylar notch. The saddle includes a first generally U-shaped stop for engaging the intercondylar notch located above the aperture a second generally U-shaped stop for engaging the intercondylar notch located below the aperture.
The alignment guide further includes a calibrated stop pivotably coupled to the body portion. The calibrated stop is movable from a first position abutting the arm to align the guide surface of the cutting block a predetermined distance from the saddle to establish said predetermined position relative to the intercondylar notch to a second position to permit the position of the cutting block to be adjusted.
According to a further aspect of the present invention, a sizer assembly is provided for determining the optimum size femoral component to couple to a resected distal end of a femur from a group of femoral components having various sizes and condyle thicknesses. The assembly includes a body portion including a flat contact surface for engaging the resected end of the femur, a plurality of feet coupled to a bottom surface of the body for engaging posterior femoral condyles to align the body portion with the resected distal end of the femur, and a stylus assembly slidably coupled to the body portion. The stylus assembly includes an arm extending proximally away from the body portion and a stylus coupled to the arm. The stylus assembly is movable relative to said body portion until the stylus engages the anterior femoral cortex. The sizer assembly also includes means on the stylus assembly and body portion for indicating the size of femoral component corresponding to the resected femur based on the position of the stylus assembly relative to the body portion. The sizer assembly further includes means coupled to the stylus assembly for supporting a drill bushing thereon corresponding to the size of the femoral component indicated by the indicating means.
The supporting means aligns the drill bushing relative to the anterior femoral cortex. The arm the drill bushing includes first and second apertures for guiding a drill to bore pilot holes in the resected femur for securing the femoral component to the resected femur.
According to a still further aspect of the present invention, an assembly is provided for aligning a cutting block relative to a resected distal end of a femur. The assembly includes a body portion having a flat contact surface for engaging the resected end of the femur, and a plurality of feet coupled to a bottom surface of the body for engaging posterior femoral condyles to align the body portion with the resected distal end of the femur. The assembly also includes a stylus assembly slidably coupled to the body portion. The stylus assembly includes an arm extending proximally away from the body portion and a stylus coupled to the arm. The stylus assembly is movable relative to said body portion until the stylus engages the anterior femoral cortex. The assembly further includes means coupled to the stylus assembly for aligning a cutting block on the resected distal end of the femur relative to the anterior femoral cortex.
According to an additional aspect of the present invention, a method is provided for reconstructing a femoral portion of a knee in a total knee replacement, the distal end of which has medial and lateral condyles and an intercondylar notch therebetween defining a distal patellar groove for articulation of the patella with the femur during flexion of a knee. The method includes the steps of securing a body portion to the distal end of the knee. The body portion is coupled to an intermedullary rod located within an intermedullary canal of a femur. The method also includes the steps of coupling a first cutting guide to the body portion, moving the first cutting guide relative to the body portion to align a guide slot of the first cutting guide at a selected location, resecting an anterior surface of the femur through the guide slot of the first cutting guide, and removing the first cutting guide from the body portion. The method further includes the steps of coupling a second cutting guide to the body portion, adjusting the position of the second cutting guide relative to the body portion to align a guide slot of the second cutting guide a predetermined distance from the intercondylar notch, securing the second cutting guide to the resected anterior portion of the femur, and cutting the distal end off the femur using the guide slot of the second cutting guide as a reference so that the femur is resected a predetermined distance proximally from the position of the intercondylar notch. The method still further includes the step of determining an appropriate size of a femoral component having a size and condylar thickness which will reconstruct the intercondylar notch at about the same distal position as the natural intercondylar notch.
The step of adjusting the position of the second cutting guide relative to the body portion includes the step of aligning a notch formed in the second cutting guide with the intercondylar notch. The guide slot of the second cutting guide is spaced said predetermined distance from the notch.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.